QOI decoder

dekoodaaja Disregard the funny repository name. There may or may not be plans to add other image decoders to this repository optimized for speed. The interface is deliberately simple, as I don’t plan to have stateful decoding or anything like that. For non color images, there might be separate decode functions. For now this is designed with std.Reader as a source and std.Writer as a sink, and the output is always rgba8888(BGRA LE) pixels. Now why this thread is titled QOI decoder, is because ...